Showing papers on "Michaelis–Menten kinetics published in 1969"
TL;DR: The commercially available bovine spleen purine nucleoside phosphorylase was compared with human erythrocytic enzyme, and in contrast to the behavior of the human enzyme, the spleen enzyme did not display the phenomena of substrate activation at high concentrations of inosine.
88 citations
TL;DR: It is concluded that the observed fatty acid composition and the preferential distribution of fatty acids in neutral fats and in phospholipids do not result from the substrate specificity of this enzyme.
46 citations
TL;DR: The l-Arabinose isomerase (l-arabinose ketol-isomerase, EC 5.4) was isolated in the crystalline state in 20% yield from the extracts of l-ARabinose-grown cells of Lactobacillus gayonii as mentioned in this paper.
42 citations
TL;DR: Phosphoenolpyruvate carboxylase from Salmonella typhimurium has been purified to homogeneity and shows a concentration-dependent aggregation in ultracentrifugal experiments.
38 citations
TL;DR: The initial velocity data obtained follow regular Michaelis-Menten kinetics without any detectable kinetic evidence for subunit interaction and the mechanism of enzyme action is ping-pong, and the first substrate is phosphoenol-pyruvate.
34 citations
TL;DR: Results indicate that a catalytic step involving general base catalysis is probably important in the carboxypeptidase-catalyzed hydrolysis of an ester and a similar set of experiments carried out on the peptide substrate gave ambiguous results.
Abstract: Solvent isotope effects have been examined for the action of the zinc-containing metalloenzyme carboxypeptidase A on ester and peptide substrates. The kinetic parameters for the carboxypeptidase-catalyzed hydrolysis of an ester, O-(trans-cinnamoyl)-L-β-phenyllactate, in 0.05 M Tris-DCl buffer containing 0.5 M NaCl at pD 8.07 and 25° were compared with those obtained from measurements done in 0.05 M Tris-HCl buffer containing 0.5 M NaCl at pH 7.52 and 25°. A (kcat)H2O/(kcat)D2O ratio of approximately 2 was obtained. The value of the Michaelis constant Km was unaffected by the change in solvent as was the inhibition constant, Ki, found for the product, L-β-phenyllactate, which is a competitive inhibitor. These results indicate that a catalytic step involving general base catalysis is probably important in the carboxypeptidase-catalyzed hydrolysis of an ester. A similar set of experiments carried out on the peptide substrate, N-(N-benzoylglycyl)-L-phenylalanine gave ambiguous results. The role of the zinc ion in the catalytic action of carboxypeptidase A can be considered in the light of these findings.
25 citations
TL;DR: The modifying effects of the cationic detergent cetyltrimethylammonium bromide (CTAB) on catalytic properties of kidney microsomal d - glucose-6-P phosphohydrolase and associated inorganic pyrophosphatase and PP 1 -glucose phosphotransferase activities have been studied, supporting the concept that CTAB acts as a “coupling” activator at lower concentrations and as a noncompetitive
25 citations
TL;DR: A purification procedure involving the solubilization of this enzyme and several additional steps led to a preparation that is homogeneous as judged by gel filtrations, sedimentation pattern, and gel electrophoresis, and the final yield was at least 25%.
23 citations
TL;DR: The pH effects on the kinetics of the yeast hexokinase reaction are consistent with the assumption that the dissociated form of the group with pK 6.8 of the central complex favours as base catalyst the release of a proton from the sugar and increases therefore the nucleophilic attack of the hydroxyl group of the sugar to the phosphoryl group of ATP.
Abstract: The kinetics of the yeast hexokinase reaction has been studied in the range of pH 6.3-9.9 at 25°. Initial velocities were determined by varying the concentrations of glucose and in dependence of ionic species of MgATP complexes, which were calculated from the total concentrations and the known equilibrium constants. Maximum velocity is decreased in the acid region due to formation of an inactive central enzyme-glucose-MgATP complex with a pK value of 6.8. In the same range the Michaelis constant for glucose decreases too, indicating that this group is protonated in the enzyme-glucose complex but not in the state of the free enzyme. In the alkaline region the Michaelis constant for glucose increases. This is caused by dissociation of a group with pK 9.9 in the free enzyme but not in the enzyme-glucose complex. The Michaelis constant for the MgATP is not altered in the acid and neutral pH regions, but is also increased in the alkaline region. This finding shows the presence of an additional site of the enzyme dissociating with a pK of 9.9. This must be in the nondissociated state for binding of MgATP. Free uncomplexed ATP acts as a competitive inhibitor of MgATP. Due to the fact, that both the uncompetitive and the noncompetitive inhibition of ATP is abolished with increasing pH, it is suggested that inhibition is caused by the ion ATPH3−. The uncompetitive part of the inhibition is also decreased in the acid region. It appears therefore that the enzyme-glucose complex can combine with the free ATP only when the group with pK 6.8 is dissociated. The pH effects on the kinetics of the yeast hexokinase reaction are consistent with the assumption that the dissociated form of the group with pK 6.8 of the central complex favours as base catalyst the release of a proton from the sugar and increases therefore the nucleophilic attack of the hydroxyl group of the sugar to the phosphoryl group of ATP.
11 citations
TL;DR: In this paper, the pH optimum of β-D-galactosidase is pH 5.5-5.0 in phosphate-citrate buffer and pH 7.0-7.5 for E. coli K 12 β-Galactoside.
Abstract: After ethanolysis of galactose with Dowex-50 as catalyst, ethyl β-D-galactofuranoside, ethyl β-D-galactopyranoside and ethyl α-D-galactopyranoside were isolated by cellulose column chromatography. m-Tolyl and guaiacol β-D-galactofuranoside were also prepared. Ethyl, phenyl, m-tolyl and guaiacol β-D-galactofuranoside were hydrolyzed by almond emulsin β-galactosidase, but not hydrolyzed by E. coli K 12 and bovine liver β-galactosidase. The kinetics of the hydrolysis of β-D-galactofuranoside by almond emulsin β-galactosidase were investigated. The pH optimum of the β-D-galactofuranoside is pH 5.0 in phosphate-citrate buffer. The Michaelis constant of phenyl β-D-galactofuranoside is 5.6×10-2M. The kinetics of the hydrolysis of corresponding β-D-galactopyranoside were also investigated. The pH optimum is pH 4.5-5.0 for almond emulsin β-galactosidase, pH 5.5 for bovine liver β-galactosidase and pH 7.0-7.5 for E. coli K 12 β-galactosidase. The Michaelis constant of phenyl β-D-galactopyranoside for almond emulsin β-galactosidase is 3.2×10-3M. The Michaelis constant of phenyl β-D-galactopyranoside is smaller than that of corresponding furanoside.
6 citations
TL;DR: 3β,17α, 21-Trihydroxypregn-5-en-20-one was a good substrate and had kinetic constants similar to those of 17α,21-dihydroxymregn-4-ene-3,20-dione, and its 17α-hydroxy derivative behaved anomalously, and their behaviour is discussed.
Abstract: The sulphate of 3β-hydroxypregn-5-en-20-one is now reported to be a substrate for crystalline 20β-hydroxysteroid: NAD oxidoreductase prepared from Streptomyces hydrogenans. Utilization of this steroid sulphate was not independent of activity towards pregn-4-ene-3,20-dione or 3β-acetoxypregn-5-en-20-one, but the total rate of reaction for equimolar mixtures of 3β-hy-droxypregn-5-en-20-one sulphate and either pregn-4-ene-3,20-dione or 3β-acetoxypregn-5-en-20-one was less than that calculated for the simplest type of mutual competitive inhibition, particularly at low substrate concentrations.
The Michaelis constant for NADH was similar (about 5 μM) with each of these compounds as substrate.
3β-Hydroxypregn-5-en-20-one, and its 17α-hydroxy derivative behaved anomalously, and their behaviour is discussed. 3β,17α,21-Trihydroxypregn-5-en-20-one was a good substrate and had kinetic constants similar to those of 17α,21-dihydroxypregn-4-ene-3,20-dione.
TL;DR: It is possible that the principal effect of lowering the dielectric constant is to increase the rate of acylation with respect to that of dissociation of Michaelis complex.
TL;DR: In Übereinstimmung mit der neu entwickelten viskosimetrischen Methode wurde die Michaelis-Menten-KonstanteK m =3,6×10−5 mmol/ml der Hydrolysenreaktion der Natriumcarboxymethylcellulose unter der katalytischen Mitwirkung von Cx-Cellulasen-Enzymen bestimmt.
Abstract: In Ubereinstimmung mit der neu entwickelten viskosimetrischen Methode wurde die Michaelis-Menten-KonstanteKm=3,6×10−5 mmol/ml der Hydrolysenreaktion der Natriumcarboxymethylcellulose unter der katalytischen Mitwirkung von Cx-Cellulasen-Enzymen bestimmt.